40 RJiPOKT 1864. 



one of the glass tubes ■whicli is fixed serving as llie chamber for explosion and 

 measurement, and the other moveable up and down on the vertical frame serving 

 to adjust the level of mercury before and after tlie experiment, and also to bring 

 the gas, after explosion, into contact with potassa for the removal of carbonic acid. 



4. For determining the amount of sulphur present in gas, use is made of the 

 ordinary process of slow combustion under a funnel-tube connected with a Liebig 

 condenser ; but an improved arrangement is adopted, by which a supply of am- 

 monia is introduced, at some didunce above thefiame, where it is free from the danger 

 of combustion, and, combining with the sulphur products of the combustion, secures 

 their retention in the collected liquid. This is effected by causing the stream of 

 water which siipplies the condenser to draw a small amoimt of air by aspiration 

 into the descending feed-pipe. This air, collected in a separate vessel, or in the 

 enlarged head of the condenser, is, by its own compressure, driven through a small 

 bottle containing dilute ammonia, and thence delivered by a slender tube into the 

 neck of the condensing tube some inches above the gas-flame. This apparatus, as 

 well as the improved eudiometer, besides their value in the ordinary routine of 

 gas inspection, may, it is thought, be of use in various laboratory experiments. 



5. The great difficulty of determining the illuminating power of gas depends, as 

 all know, on the want of a reliable and imiform standard of light to which to 

 refer. The imcertainty of the ordinary photometric determinations, by the use of 

 the standard candle, resulting from the imavoidable variability of the candle, is 

 further increased by the fact, that the unit is so small that the observer is confined 

 to the part of the scale where a very slight change in the position of the disk 

 makes a great difference in the reading. To secure a more uniform light, and a 

 larger unit of comparison. Professor Rogers has used a kerosene lamp with a flat 

 flame, limited at the sides and top by a strip of platinum foil. This he found 

 capable of affording a very uniform disk of light equal to about 1\ candles. The 

 lamp is supported in a balance of pecidiar construction, enabling the observer to 

 mark exactly the rate at which the oil is consumed in each stage of the experi- 

 ment, and to make such corrections as are needed on this account. Although far 

 from affording a perfect standard, this arrangement promises much more satis- 

 factory results than the ordinary method of observation. 



Neither of the chemical processes referred to were put forward as replacing the 

 refined and e.xact methods of gaseous analysis with which chemists are fiimiliar. 

 They have been found convenient for the purposes of ordinary gas inspection, and 

 are of such accuracy as not only to serve this object, but to prove usefid in the 

 laboratory assays where the highest degi-ee of exactness is not demanded. 



In conclusion. Professor Rogers made a brief reference to his experiments on the 

 influence exerted by the presence of carbonic acid in gas on its illuminating power. 

 He found that even the small amount of this impurity, which in some manufac- 

 tories is allowed to remain in the gas, produces a sensible diminution of the light. 

 The effect varies with the quality of the illuminating gas, and was found to range 

 from three to nearly five per cent, of the illuminating pow;er for each per cent, 

 of carbonic acid present in the mixture. In a series of experiments with gas 

 successively mingled with larger and larger quantities of carbonic acid, it was 

 found that 58 per cent, of carbonic acid, although it did not prevent combustion, 

 rendered the flame so dim as to be inappreciable on the photometric screen. 



On an Invention hy Mr. Cornelius, of Philadeljyhia, for Lighting Gas by 

 Electricity. By Professor W. B. Eogeks. 



The electrical apparatus was attached to a common gas-burner. It was an ap- 

 plication of the principle of frictional electricity (the apparatus being a modified 

 form of electrophorus), and, on the removal of a stopper of vulcanite, the friction 

 generated an electric chai-ge, and the gas was instantly ignited. It could be ar- 

 ranged so as at the same instant to light the whole of the burners in a room. 



Contribntio')iS towards the Foundation of Quantitative Photography. 

 By Professor Eoscoe, B.A., Ph.D., F.B.S., F.C'.S. 

 Our knowledge of the photographic processes has, as yet, attained only the quali- 



